One-dimensional seepage in unsaturated, expansive soils

This study presents a new nonlinear partial differential equation to describe the dissipation of suction within unsaturated, swelling soils by vertical moisture flow using a material coordinate and soil parameters defined by constitutive surfaces from volume change theory. The equation takes a form similar to two classic equations that describe the flow of water within a soil matrix but accounts for the soil’s interactions: the soil structure, water phase, suction, and stress. This new equation may simplify to Richards’ equation for unsaturated flow through rigid media and to Terzaghi’s consolidation equation under appropriate conditions. Although intended for unsaturated, swelling soils, this new equation may be applied to describe the vertical dissipation of pore pressures for all soils: saturated or unsaturated and rigid or nonrigid. Lastly, several simulations showed that the use of Richards’ equation overestimates the rate of suction dissipation in swelling soils.